1. Field of the Invention
The present invention relates to a vent structure of a motor, in particular, a closed type electric motor.
2. Description of the Related Art
In general, a motor used above water is a sealed type motor constructed to be watertight. In such a motor, a motor case is heated by a heat generated by rotation of an armature. At this time, thermally expanded air in the motor case passes through a clearance 4 between a core wire 2 of a lead wire 1 and and a cover 3 thereof shown in prior art FIG. 5 and FIG. 6, and then, is discharged outside via an opening end portion 3A of the cover 3. On the other hand, when the interior of the motor case is to be cooled, air is sucked into the motor case from the opening end portion 3A of the cover 3 of the lead wire 1 through the clearance 4 (first prior art).
There is another known sealed type motor which is constructed in a manner that the opening end portion 3A of the cover 3 of the lead wire 1 is sealed or molded with the use of a bonding agent so as to fully watertightly and airtightly seal between the interior of the motor and the outside (second prior art).
The aforesaid sealed type motor of the first prior art has the following problems. Specifically, water adheres to a terminal 5 which is fixed to an end portion of the core wire 2 of the lead wire 1 by pressing, and when an atmospheric moisture is high, a water vapor is condensed into water in the clearance 4 between the core wire 2 of the lead wire 1 and the cover 3 thereof; as a result, the water adheres thereto. The water is sucked into the motor case together with the air, and then, is collected therein; as a result, the water contacts the armature and the brushes of the motor. Thereafter, due to the influence of water, copper of the armature is precipitated onto the brushes by electrolysis. As a result, the armature and the brushes are damaged; for this reason, there is the possibility that a abnormal abrasion, and wear is caused between the armature and brushes.
In the sealed type motor of the second prior art, moisture and air do not flow into the interior of the motor case and flow out therefrom; for this reason, the motor case has an absence of moisture and oxygen. As a result, there is the possibility that abnormal dust abrasion is caused between the commutator and the brushes.
In the aforesaid sealed type motor of the second prior art, in order to prevent the aforesaid dust abrasion, electric graphite is used for the brushes, and there has been proposed brushes made of a material impregnated non-hygroscopic metallic halogen salt. However, these materials increase the cost of construction.